The present invention generally relates to a magnetically operated actuator and, more particularly, to the magnetically operated actuator suited for actuating an operating element such as used in, for example, a photographic shutter mechanism, a photographic aperture mechanism, a high-speed on-off electric switch assembly, an electromagnetically operated needle selector used in a knitting machine or any other machine component required to be operated in response to the application of an electric enabling signal.
Numerous magnetically operated actuators for actuating or operating an operating element by the utilization of an interaction between the electromagnet and the permanent magnet are currently commercially available, an example of which is disclosed in, for example, the Japanese Laid-open Patent Publication No. 59-199850, first published Nov. 13, 1984.
All of these prior art magnetically operated actuators make use of a combination of electromagnet and permanent magnet, and the interaction between the magnetic force emanating from the electromagnet, then electrically energized, and the magnetic force emanating from the permanent magnet is utilized to drive the operating element between two spaced apart operative positions. Therefore, in the event of the failure to supply an electric current through a solenoid used in the electromagnet, the interaction between the electromagnet and the permanent magnet no longer occur with the consequence that the movement of the operating element may become insecure. By way of example, in a particular application where the supply of an electric current to the magnetically operated actuator is controlled according to a program uploaded in a programmable computer, the supply of the electric current has to be continued during at least a period of time required for the operating element being moved to reach one of the operative positions. In reality, however, the operating element having reached the operative position and, therefore, impinged upon a stopper defining such respective operative position tends to rebound from the stopper, exhibiting a bouncing motion that attenuates progressively with passage of t time, and, therefore, the periof of t time during which the electric power is required to be actually supplied to the electromagnet is necessarily longer than that required for the operating element to be brought into initial contact with the stopper so that the bouncing motion can be quickly minimized or the attenuation thereof can be accelerated.
Moreover, where the number of the operating elements is increased to provide a multistage actuating capability, and in the event that one of the operating elements then impinging upon the associated stopper undergoes the bouncing motion, the neighboring operating element or elements may be adversely affected by the bouncing motion of such one of the operating element in such a way as to result in an unwanted movement or as to fail to operate properly. Once this happens, the time required for the electric current to be supplied to the electromagnet may be necessarily prolonged to substantially avoid any possible interference of bouncing motion from one operating element to the neighboring operating element or elements.
In view of the foregoing, the currently available, high-performance magnetically operated actuator requires the supply of the electric power for a relatively great length of time, for example, 7 to 10 milliseconds, in order for the operating element to be driven in one direction. This is undesirable not only because a relatively large amount of electric power is consumed, but also because a relatively great amount of heat is generated from the solenoid unit used in the electromagnet assembly. Furthermore, according to the prior art, cases may often happen wherein the above discussed problems cannot be obviated even with the prolonged supply of the electric power.
Apart from the problems inherent in the prior art magnetically operated actuators, the recent trend in the field of industrial machines is that the high speed performance of the operating element is desired to improve the work efficiency. Another demand in the market is for a multistage actuating capability wherein a plurality of operating elements and a corresponding number of drives are combined in a single magnetically operated actuator so that the magnetically operated actuator as a whole can have an improved high-speed performance. Furthermore, the applicability of the magnetically operated actuator in a plural number to meet value-added requirements in the market is also desired for.
However, the use of the plural magnetically operated actuators together with the increase number of the drives connected parallel to each other results in the use of the increased number of the solenoid units which in turn results in the generation of an increased amount of heat from the assembly as a whole. This means that, in order for the discharge of the resultant heat to be facilitated, a relatively large surface area is required for the radiation of the heat and, therefore, the assembly tends to become bulky in size. Specifically, the assembly requires the use of an increased number of heat radiating fins and/or of a forced draft system to facilitate the discharge of heat emitted from the assembly as a whole, resulting in the increased size and cost of the assembly as a whole.
The reduction in number or time of supply of the electric current through the solenoid unit used in the magnetically operated actuator may reduce the amount of heat emitted from the assembly as a whole. However, the reduced number of supply of the electric current results in a loss of the high-speed movement of the operating element and, on the other hand, the reduction in time during which the electric power is supplied results in the unstable movement of the operating element.
The more recent version of the magnetically operated actuator designed to improve the response of the device to the application of an electric current and also to stabilize the movement of the operating element is disclosed in, for example, the Japanese Laid-open Patent Publication No. 61-237325, published Oct. 22, 1986, (which publication corresponds to the U.S. Pat. No. 4,658,230, issued Apr. 14, 1987, to the same inventor as the present invention).
According to this Japanese publication or its U.S. counterpart, there is disclosed a magnetically operated actuator which comprises a generally elongated operating element; an electromagnet assembly for driving the operating element to displace between first and second positions under the influence of magnetism emanating therefrom, said electromagnet assembly comprising an iron core and a solenoid unit disposed around the iron core; a permanent magnet assembly rigidly mounted on the operating element and having a pair of magnetic poles opposite in polarity to each other and having a magnetic field which is developed between the opposite poles; and a stopper member for restricting the stroke of movement of the operating element between the first and second positions. The electromagnet assembly is fixedly supported in position with one of the opposite ends of the iron core situated in the magnetic field developed between the poles of the permanent magnet assembly. The first and second positions are located in the vicinity of the opposite poles of the permanent magnet assembly.